Abstract/Summary

Although microscope analysis is very useful for studying phytoplankton communitycomposition, it does not allow for high frequency (spatial and/or temporal) data acquisi-tion. In an attempt to overcome this issue, ﬂuorescence-based approaches that useselective excitation of pigment antennae have spread rapidly. However, the ability of spectral ﬂuorescence to provide accurate estimates of phytoplankton biomass andcomposition is still debated, and only a few datasets have been tested to date.In this study, we sampled of a wide range of water bodies (n¼50) in the Ile-de-Franceregion (North Central France). We used the resulting extensive dataset to assess theability of the bbe-Moldaenke FluoroProbe II (FP) to estimate phytoplankton communitycomposition in lakes and reservoirs.We demonstrated that FP data yields better estimates of total phytoplankton biovolumethan do spectrophotometric chlorophyllameasures and that FP data can be further cor-rected using the average chlorophyllato biovolume ratio among phytoplankton groups.Overall, group-speciﬁc relationships between FP and biovolume data were consistent.However, we identiﬁed a number of cases where caution is required. We found thatEuglenophytes are expected to depart from the global FPvs.biovolume relationship of the‘green’ group due to varying Fv/Fm and pigment content in response to environmentalconditions (photoautotrophicvs.photoheterotrophic growth). Then, it appears necessaryto consider the composition of the Chromophytes community in order to obtain a goodagreement between both biomass estimation methods. Finally, we conﬁrmed the misat-tribution toward the ‘red’ group of phycoerythrin-containing cyanobacteria and theoccurrence of a strong scattering in the relationship between the FPvs.biovolume of the‘blue’ group that can be partly attributed to the occurrence of large colony-forming cya-nobacteria (e.g.,Microcystisspp,Aphanizomenon ﬂos-aquae).We propose correcting procedures to improve the quality of data obtained from spectral ﬂuorescence tools in the context of large-scale sampling of lakes and reservoirs.